Computational Fluid Dynamics Analysis for Evaluating the Urban Heat Island Effects

The quality of the thermal environment within the built environment is dependent by local climate and urban design features. Therefore, the scientific knowledge on urban design and microclimate are fundamental for obtaining a tolerable thermal environment at the neighborhood scale. Such problematic interested the huge part of the world population that lives in urban area, which is currently about 50% and it is expected will increase to 66 % by 2050. The specificity of the urban climate is frequently associated with the urban heat islands phenomenon, which refers to the elevated temperatures within the city areas compared to the rural surroundings. In this context a typical urban geometry is represented by the so called “urban canyon “that denotes an ideal infinite urban street confined by buildings on both sides In this study an urban geometry, constituted by three urban street canyons with a canyon aspect ratio H/W of 1.0, has been examined. CFD simulations were performed to evaluate the fields of temperature and velocity of the air within the urban canyons and their surroundings. Several scenarios were examined considering alternatively the leeward or the windward walls hitted by the sunrays, while the opposite façade was shaded, as well as varying the reflective properties of the surfaces and the wind velocity. The results of simulations evidence that the adoption of materials of the building envelope with high albedo coefficient guarantees a decrease of the temperatures at least of 1.5°C. Therefore, an increase of the knowledge of urban climate may provide valuable contribution to promote energy efficiency in the built environment.